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PTFE An Introduction

An introduction to Chemours Fluoropolymers,

part of Chemours Chemicals & Fluoroproducts

Polytetrafluoroethylene (PTFE) is produced by the polymerization of tetrafluoroethylene (TFE) monomer yielding a perfluorinated straight-chain high molecular weight polymer with unique properties. TFE is polymerized by two different processes i.e. granular (also called suspension) polymerization and aqueous dispersion (emulsion) polymerization. In general, PTFE resins are homopolymers of tetrafluoroethylene, or in some special cases, modified homopolymers containing very small amounts (less than 1 percent) of an additional perfluorinated monomer. Modified homopolymers have special processing and/or end-use characteristics while maintaining the outstanding properties of PTFE.

Many of the unique properties can be explained by the molecular structure of PTFE. The carbon-carbon bonds, which form the backbone of the polymer chain and the carbonfluorine bonds are extremely strong. The fluorine atoms form a regular, protective sheath over the chain of carbon atoms, this sheath protects the polymer molecule from chemical attack. It also reduces the surface energy resulting in a low coefficient of friction and non-stick properties.

In order to achieve the desired properties such as toughness and green strength very high molecular weight is needed (in range of 106 to 107) resulting in an extremely high melt viscosity (1 to 100 GPa.s or 1010 to 1012 P). The material will not flow above its crystalline melting point. Consequently PTFE could not be fabricated by conventional thermoplastic techniques. High molecular weight polytetrafluoroethylene is manufactured and sold by Chemours in four main types i.e. granular moulding powder, Fine powder and aqueous dispersion each requiring different fabrication techniques. Furthermore each of the three main types is subdivided into a number of grades to suit various end-uses more precisely.

PTFE Aqueous dispersions are milky white dispersions of PTFE particles suspended in aqueous medium, stabilized by wetting agents. The dispersion typically contains 30 up to 60 weight % polymer particles and some surfactant. The PTFE particle characteristics and surfactant type depend on the application. They can be further formulated to meet specific needs by adding other solid or liquid ingredients.

PTFE Aqueous dispersions are applied to substrates by spraying, dipping or impregnation. After applying the dispersion on the substrate the water and surfactants are removed by evaporation and the PTFE is sintered. The substrate needs to be resistant to the typical sintering temperatures of PTFE. In special cases, such as impregnated packing, the PTFE is left unsintered to maintain flexibility.

PTFE Aqueous dispersion can also be used as additive in thermoplastics (as drip suppressant) or in dusty products to eliminate dust. As with PTFE Fine powders, aqueous dispersion particles also fibrillate under shear and these PTFE fibrils form a web within the host material that holds the dust or avoid the dripping of burning droplets in case of a fire.

PTFE has an extremely low coefficient of friction. Values of 0,02 have been reported.

The lowest values are obtained under condition of high pressure (> 3 MPa) and low velocity (< 0,1 m/min).

Due to its very low surface energy (18,5 mN/m) PTFE has excellent anti-stick properties.

Industrial products made with Chemours fluoropolymer resins have exceptional resistance to low as well as high temperatures, chemical reaction, corrosion, and stress-cracking. The properties of Chemours fluoropolymer make it the preferred plastic for a host of industrial applications for one of the following reasons:

• Lowest coefficient of friction of any solid material

• Static coefficient of friction is lower than dynamic coefficient of friction

• Ability to operate without lubrication or in marginally lubricated conditions

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